I've been working on squatting recently, after going through a realization that it is really important to get your hips below your knees when you squat I've been trying to attain a full range of motion, ass to grass squat.
That being said, as part of my workouts, I've been squatting with no weight, stretching all of the muscles I need to get deeper (hip flexors, quads, calfs, etc).
I've been doing box squats and lowering it as I get small gains in flexibility. I'm to the point where the box is ~6 in below my knee while standing upright but I'm realizing that it is going to take a while - maybe years - for me to gain that flexibility. I've been going at this for a few months and even though I have small gains I'm to the point where progress is in centimeters/millimeters.
I'm pretty sure that this is a flexibility issue and not just bad form. For example, if I lay on my side with my legs in line with my torso and try to pull one foot straight back, I can't get my heel to touch my glutes. Also, many years ago, I did give myself a knee injury (damaged left meniscus) by trying to go deeper so now I'm very familiar with what a bad squat feels like and have a good sense of how my knees should feel when I'm going down.
So - with all of that being said - should I continue developing range of motion with no weight, or am I at a point where I can/should begin adding weight to my squats?